Brightening bath



Patented Oct. 21, 1952 BRIGHTENING BATH Harold 'J. Reindl and Stanley R. Prance, Dayton,

Ohio, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware NoDrawing. Application October 20, 1950, Serial No. 191,324

I This invention relates to chemical dipping processes and is particularly directed to dipping processes for brightening the surface of aluminum and/or aluminum alloys.

It is, therefore, a primary object of theinvent1on to provide a chemical brightening bathfor use in connection with aluminum and/or alumia chemical brightening bath for use in connection with aluminum and/or aluminum alloys which has substantial brightening effects when using very low concentrations of the chemicals therein, said bath being of a substantially watery I consistency that minimizes drag-out loss and which facilitates rinsing.

Further obiects will be apparent from the following description. I

The use of nitric acid-hydrofluoric acid baths for brightening aluminum and/or aluminum alloys is well known in the art, such baths create numerous industrial hazards and problems through the use of the hydrofluoric acid per se. On the other hand, nitric acid-hydrofluoric acid baths, clue to the strong conjoint action of the specific acids, may be used in quite dilute condition which minimizes other production problems, for example, drag-out loss and likewise makes the rinsin of the brightened articles a relatively easy, matter as compared with the usual syrupy phosphoric acid type of brightening baths.

Due to the strength of a nitric acid-hydrofluoric acid combination and the ability to use such a combination in low concentrations, the cost of the bath is reduced. mak ng a bath of this type very desirable commercially.

copper fluoride, etc, silver or gold salts, etc., plus a brightener such as ethylene glycol. These in- 7 Claims. (01. 4142) gredients may be contained in a stainless steel tank and will have excellent brightening action on aluminum and/or aluminum alloys. In fact, the action will be greatly improved over a bath utilizing nitric acid and hydrofluoric acid per se. Furthermore, we have found that the use of ammonium bifluoride extends the life of the: bath in addition to yielding improved results from a brightening standpoint. In all cases, the-ammonium salt of the hydrofluoric acid either as a fluoride or bifluoride gives improved results over the use of hydrofluoric acid per se even when the hydrofluoric acid is combined with other ingredients to form a salt in situ within the solution. In this connection, the improved result is probably due to the fact that the addition of ammonium fluoride or ammonium bifluoride to the bath yields the ammonium salt ofthe hydrofluoric acid in complete combinationwith no free hydrofluoric acid nor free ammonium hydroxide or other combining reagent present. If hydrofluoric acid per se is added to the bath,its combining action with other ingredients to yield salts is never complete unless definite molar quantities of all ingredients are added to assure complete reaction. Obviously, this is impossible in a commercial operation and therefore there is always an excess of the hydrofluoric acid or an Range Preferred Percent Percent Commercial nitric acid 2. 0 -7. 5 3. Ammonium bifiuoride .30 .75 65 Ethylene glvcol .40 l. 0 .60 Ohromic acid (ClOs) .30 75 .65 Soluble metallic salt (copper nitrate).. .002- .05 0025 Water Remainder Remainder This bath may be modified by using cane sugar dissolved in the bath in place of ethylene glycol within the range of 20% to 1.0% with a 30% preferred and similarly ammonium fluoride may be used in place of ammonium bifluoride within the same ranges. The bath is made up with water as a base and is operated at an elevated temperature, for example, in the order of F. to 212 F. The aluminum parts to be brightened are cleaned so as to be free from grease and are then immersed in the hot brightening bath for a period ranging from 3 to 5 minutes depending upon the finish desired, after which they are removed from the bath and thoroughly rinsed in water to remove many traces of the bath therefrom. They may then be dried by preferably dipping in hot water, followed by an air dry With or Without air blast.

We have found that a brightening bat of the character described herein has good life and that the drag-out loss, due to the low Viscosity of the watery solution, is maintained at a minimum. In order to keep the bath at an operatinglevel, We add additional ingredients periodically .during use as needed (this may bedetermined by the brightness of the parts being treated or by analysis of bath concentrations) in the'following concentrations: for each square foot of surface brightened We add in the order of 8.5 cc..nitric acid, .75 gram of ammonium bifiuoride and .75cc. of ethylene-'glycolor .4 gram .of sugar. Water may be added simultaneouslytomaintain the level of the bath to a givenpoint within the brightening tank.

It is to be, pointed out here that our improvements over prior art type of brighteners are directed to the use of ammonium fiuorideand particularly to the use of ammonium bifluoride together with the addition of ethylene glycol or sugar as a brightener. These improvements yield a better brightening solution. for .thefollowing reasons:

1. The brightening action of the bath is better;

2.,The control oithe bath is moreeasily maintained;

.3. The commercial hazards .of the bathare minimized; and

4. The costof the .bathlisreduced.

WhiIethe embodiments of the .present'invention as herein disclosed, constitute preferred forms, it is to be understood that other iorms might be adopted.

gredients ammonium bifluoride to ..75%,. nitric-acid 2.0% to 7.5%, chromic acid 30% to .75% and ethyleneglycol A092; .to 1.0% and wherein water makes upsubstantially .the.re-

mainder of the bath.

2. A bath as claimed in claiml with:the...added ingredient of a salt oi a metalbelow hydrogen in the electro-chemical series, .002% to 05% 3. A brightening bath for use in connection ,with aluminum and/or aluminum alloys Wherein the brightening is carried out at a temperature varying between 185 F. to 212 F. consisting of a solution having as its basic ingredients ammonium bifluoride nitric acid 3.75%, chromic acid .65% and ethylene glycol .60% together with water which makes up substantially the remainder of the bath.

i. A brightening bath for use .in-.connection with aluminum and/or aluminum alloys Wherein the brightening is carried out at a temperature varying between 185 F. to 212 F. for a .periodranging from 3 to 5 minutes, consisting of; an aqueous solution having as its basic ingredients ammonium bifluoride .65%, nitric acid ..3.75%,..chromic acid 55%, ethylene glycol .60%

together with traces of copper nitrate.

.5. Abrightening bath for use in connection with'aluminum and/or aluminum alloys Wherein thebrightening is carried out at a temperature varying between 185. -F. to 212 F. consisting of; a solutionhaving as its basic ingredients ammonium'bifiuoride 550% to nitricacid 2.0% 'to 7.5%, chromic acid.;30% to .75% and cane sugar 20% to 1.0% and wherein water makes up substantially Lthe remainder of :the

bath.

6. A brightening bath .for use in connection with aluminum and/or aluminum alloys wherein the brightening is carried out at atemperature varying between.185 F. to 212 F. consisting of; a solution having as its basic ingredients ammonium bifiuoride 465%;nitric acidf3'.75%, chromic acid .65%'and cane sugar 30% together with water which makes'up 'substantially'the remainder of the bath.

7. A brightening bath foruse in "connection with aluminum and/or aluminum'alloyswherein the brightening is carried out at a'temperature varying between 185 F. to '212"F.fora period ranging from'3 to ,5 minutes, consisting of; an aqueous solution having as its basic ingredients ammonium bifiuoride ;65%,'nitriciacid 3.75%, chromic acid .65'%, cane sugar together with traces of coppernitrate.

HAROLD J. REINDL. STANLEY R. PR-ANCE.

I REFERENCES CITED The following references are of record in the file of this patent:

UNITED. STATES PATENTS Number Name Date 590,966 Cornwall Oct. 5,1897 "2,168,909 Mason Aug."8, 1939 2,393,875 Van Dusen Jan; 29, 1946 2,415,724 Beall Feb.'11,'1947 2,507,314 Mason May '9, 1950 

1. A BRIGHTENING BATH FOR USE IN CONNECTION WITH ALUMINUM AND/OR ALUMINUM ALLOYS WHEREIN THE BRIGHTENING IS CARRIED OUT AT A TEMPERATURE VARYING BETWEEN 185* F. TO 212* F. CONSISTING OF; A SOLUTION HAVING AS ITS BASIC INGREDIENTS AMMONIUM BIFLUORIDE .30% TO .75%, NITRIC ACID 2.0% TO 7.5%, CHROMIC ACID .30% TO .75% AND ETHYLENE GLYCOL .40% TO 1.0% AND WHEREIN WATER MAKES UP SUBSTANTIALLY THE REMAINDER OF THE BATH. 